The invention concerns a hydraulic line coupling arrangement of a consumer, with a pump line, a tank line and a safety valve in the pump line, the valve element of the safety valve being acted upon in the opening direction by an opening pressure from the pump line and in the closing direction by a closing pressure of a closing pressure connection.
A line coupling arrangement of this kind is known from the previous German patent application 199 22 866.3. When the consumer is connected with a supplier, the inlet valves of the pump line and the tank line are opened, so that the pressure in the pump line can get from the supplier to the consumer and the hydraulic fluid displaced by this can get back to the supplier via the tank line. Application examples for a hydraulic line coupling of this kind are tractors and other agricultural machines with different attachments, the attachments, for example a revolving mower or a loader wagon, requiring not only a mechanical connection with the tractor but also a hydraulic supply. When, in connection with such a line coupling, the tank line is not correctly connected with the supplier, the tank line is closed at the supplier end. Accordingly, the pump pressure in the tank line increases and closes the safety valve, so that the hydraulic attachments of the consumer connected downstream of the safety valve are not loaded by the pump pressure for a long time.
DE 38 16 987 C1 shows a safety valve for a line coupling arrangement, which is installed on the consumer. This safety valve blocks a pump line for as long as a coupling connection to the tank line of the consumer has not been established. When establishing this coupling connection, not only the valves at both ends of the tank line of supplier and consumer are opened, but also a pressure decrease is caused on the closing side of the safety valve via a valve operated mechanically by means of a tappet, so that the pump pressure can move the safety valve to the open position.
DE 37 28 986 A1 shows another safety valve for hydraulic rotary drives, said valve also being arranged on the supplier. On the tank coupling, that is, the coupling part connecting the tank line of the consumer with the tank line of the supplier, a valve slide is provided, which is displaced on the establishment of the coupling connection. As long as this valve slide has not yet-been displaced, it ensures a connection of the tank line to a branch of the pump line of the supplier, so that hydraulic fluid still remaining in the supplier can flow back to the tank.
The invention is based on the task of preventing an overloading of the consumer in connection with an incorrect coupling.
In the hydraulic line coupling arrangement mentioned in the introduction, this task is solved in that a pilot valve is provided for controlling the closing pressure, the position of the pilot valve being controlled by the pressure in the tank line.
Thus, it is possible to fit the safety valve in or at the consumer, that is, the safety measures for the consumer and its hydraulic attachments can be provided in the immediate proximity of the consumer. The safety arrangement, that is, the safety valve can be directly adapted to the requirements of the individual consumer, for example the possible maximum pressure, which should be permissible, also in case of errors, which is not possible when the safety valve is arranged at the supplier supplying varying consumers. The use of the pilot valve involves a higher degree of freedom in connection with the selection and embodiment of the closing pressure. In case of errors, the pilot valve ensures a very quick building up of the required closing pressure for the safety valve.
It is preferred that in the closing direction the valve element is loaded by a spring, the pilot valve being controllable in such a way that the pressure of the pump line also acts in the closing direction. Normally, it must be assumed that the pressure in the pump line is the highest pressure in the consumer. Enabling this pressure also to act in the closing direction initially causes the establishment of an equilibrium on the valve element. By means of the spring force, the valve element can be moved to its closing position. Thus, it is possible for the valve element to perform both its opening movement and its closing movement relatively fast, as the valve element is acted upon by the higher of the ruling pressures.
In a first alternative it is provided that the pump line is connected with the closing pressure connection via a throttle, the pilot valve releasing or blocking a connection between the closing pressure connection and the tank line. When the pilot valve releases the connection between the closing pressure connection and the tank line, the pressure available at the closing pressure connection is the same as the pressure available in the tank line. The throttle then produces a pressure drop, which corresponds to the pressure difference between the pump line and the tank line. The valve element of the safety valve remains open, as it is acted upon in the opening direction by the pressure in the pump line. When now the pilot valve closes, firstly the connection between the closing pressure connection and the tank line is blocked. At the same time, however, hydraulic fluid from the pump line reaches the closing pressure connection via the throttle, that is, very quickly the pressure of the pump line will also be available at the closing pressure connection, this pressure, together with the spring, displacing the valve element to its closing position.
In an alternative embodiment it is provided that the pilot valve is made as a three-way valve, which in one position connects the pump line with the closing pressure connection and in another position connects the closing pressure connection with the tank line. When the closing pressure connection is connected with the tank line, the pressure in the tank line is also available at the closing pressure connection, that is, the safety valve is open, as the pressure acting upon the valve element in the opening direction is higher than the pressure in the closing direction. When, however, the pilot valve is changed over, the pressure in the pump line reaches the closing pressure connection directly, so that the safety valve is closed.
Preferably, the pilot valve is acted upon by a spring against the direction of the pressure of the tank line in the direction of a position, in which the closing pressure connection is connected with the tank line. In a manner of speaking, this position is the position for the normal operation, during which the tank pressure of the supplier is available in the tank line of the consumer. In this case, the force of the spring on the pilot valve is higher than the force, which the pressure in the tank line can produce. When, however, the tank line is no longer or not correctly connected with the tank line of the supplier, be it through a released or not correctly connected coupling, hydraulic fluid can no longer or not to a sufficient degree flow off through the tank line, so that the pressure in the tank line increases. As soon as the pressure in the tank line is so high that it overcomes the force of the spring on the pilot valve, the pilot valve is changed over, which immediately causes the closing of the safety valve.
Preferably, the consumer has a consumer tank. This provides an additional measure that may cause a pressure release in the consumer. The consumer tank does not have to be big. It is sufficient, when the consumer tank can hold a hydraulic fluid quantity, which has to be drained off from the consumer or its attachments, respectively, to initiate a desired pressure decrease after the closing of the safety valve.
In this connection, it is preferred that the tank line is connected with the consumer tank via a safety valve. During xe2x80x9cnormal operationxe2x80x9d the safety valve ensures that no hydraulic fluid flows off into the consumer tank. This will not happen until the pressure in the tank line exceeds a predetermined value. The safety valve releases at a pressure that is higher than the pressure required for the adjustment of the pilot valve.
It is also preferred that a control connection on the spring loaded side of the pilot valve is connected with the consumer tank. In this connection it is taken into consideration that on the one hand certain leakages may occur at the pilot valve and on the other hand the hydraulic fluid required for the control of the pilot valve also has to be displaced to somewhere.
Preferably, the opening pressure is available in an opening pressure connection, which is connected with the inlet and the outlet of the safety valve. Independently of the position of the valve element of the safety valve, an opening pressure is thus always available, so that after eliminating the error in the tank coupling line the valve element can always be returned to its opening position again.